Flush valves may have a handle that, when manipulated, pushes an actuator which, in turn, opens a bypass valve within a piston in the flush valve. By opening the bypass valve, pressure above the piston drops and allows line pressure to lift the piston from its seat within the flush valve and channel water to flush a toilet, urinal or the like. While the toilet or urinal fixture is being flushed, line pressure is also directed above the piston increasing the pressure in this area. As pressure equalizes above and below the piston, the piston seats itself within the flush valve and stops flow therethrough.
As water shortages are experienced and anticipated, water conservation efforts are being pushed by local governments and concerned citizens. Many toilets have dual flush mechanisms that provide greater amounts of water if greater amounts of flow are required. Some control the amount of water electronically with solenoid valves, others use timers and the like to measure the amount of flow through a valve. Some use two levers to control amounts of flows, other use motion detectors and sense the amount of time a fixture is used to control flow.